Technical Field
The present disclosure relates to a light-emitting device and a method of manufacturing the same, and more particularly, to a chip-scale packaging light-emitting device having a beveled chip reflector and a method of manufacturing the same.
Description of the Related Art
Light-emitting devices (LEDs) are commonly used as light sources for illumination, backlighting, or indicators, and light-emitting semiconductor dies are typically disposed inside a package structure to become an LED package or further encapsulated or covered by photoluminescent materials as a white LED package.
Through a proper design, an LED can achieve good luminous efficacy. For example, as shown in FIG. 1, the LED is a Plastic Leaded Chip Carrier (PLCC) LED package, which generally includes a horizontal light-emitting semiconductor die 80 and a lead frame structure 81. The light-emitting semiconductor die 80 is electrically connected to the lead frame structure 81 through a gold wire 82. The lead frame structure 81 includes a reflective cup 811 to reflect the light inside the package toward a light-emitting surface of the package. Although the luminous efficacy of the PLCC LED package can be effectively increased through the reflective cup 811 with a beveled reflective surface surrounding the light-emitting semiconductor die 80, the PLCC LED package has its inherent limitations, including: (1) large differences in paths of the primary light emitted from the light-emitting semiconductor die 80 travelling in a photoluminescent material along various radiation angles resulting in poor color uniformity, and ultimately resulting in yellow halo ring; (2) the light-emitting area of the LED package is much larger than the light-emitting semiconductor die area, resulting in a larger etendue, so that a design of a secondary optical lens to shape the radiation pattern is not easy; and (3) large thermal resistance of the lead frame structure 81 will cause heat dissipation to be ineffective and eventually lead to decay of luminous efficacy.
With the evolution of LED technology, chip-scale packaging (CSP) of an LED has drawn great attention in recent years due to its advantages. The CSP LED has the following benefits compared with the PLCC LED package because the CSP LED comprises a flip-chip light-emitting semiconductor die and a packaging structure covering the light-emitting semiconductor die (usually including a photoluminescent material inside the packaging structure). (1) Omission of gold wires and extra lead frame or submount, and thus a CSP LED significantly reduces material costs. (2) Due to the omission of the lead frame or submount, the thermal resistance between the light-emitting semiconductor die and a heat sink can be further reduced so that under the same operating conditions it will have lower operating temperature. (3) A lower operating temperature allows the light-emitting semiconductor die to have higher quantum efficiency. (4) A greatly reduced package size allows more flexible design of an LED module or luminaire. (5) A CSP LED has a smaller light radiation area. Thus the etendue can be reduced, facilitating the design of secondary optics to shape the radiation pattern, or to obtain higher luminescent intensity.
Taking a white-light CSP LED as an example, it can generally be categorized into two types of CSP LEDs according to the viewing angle of light radiation. The first type is a “five-surface emitting” CSP LED device, which comprises a flip-chip light-emitting semiconductor die and a photoluminescent layer covering the light-emitting semiconductor die. The photoluminescent layer covers the chip-upper surface and the four chip-edge surfaces of the light-emitting semiconductor die. This type of CSP LED emits light from its top and four side surfaces, that is, it radiates light from five surfaces along different directions, and hence is five-surface emitting. Depending on the aspect ratio of the external dimensions, the viewing angle of the five-surface emitting CSP LED generally ranges from 140 degrees to 160 degrees. Because of its large viewing angle, it is suitable for applications specifying a larger angle illumination, such as luminaire lighting, direct-lit backlight module, and so forth.
The second type is a “top-surface emitting” CSP LED, which comprises a flip-chip light-emitting semiconductor die, a photoluminescent layer and a reflective structure. The photoluminescent layer is disposed on top of the light-emitting semiconductor die, whereas the reflective structure is disposed surrounding the light-emitting semiconductor die. That is, the reflective structure is disposed to surround and cover the four edge surfaces of the light-emitting semiconductor die. Since the reflective structure can reflect the light emitted from the light-emitting semiconductor die and the photoluminescent layer from the four sides back into the package structure, the CSP LED can emit light solely or primarily from the top surface of the CSP LED, and hence is top-surface emitting. The top-surface emitting CSP LED typically has a viewing angle between 115 and 125 degrees, providing a smaller angle of illumination for applications specifying directional lighting, such as spotlights and edge-lit LED backlight modules.
However, as the size of the CSP LED shrinks, the manufacturing techniques that can usually be utilized to form LEDs, such as the beveled reflector design of the PLCC LED package, will become difficult to be applied to the CSP LEDs. For example, in the top-surface emitting CSP LED, the reflective structure generally completely covers the chip-edge surfaces of the light-emitting semiconductor die and/or the edge surfaces of the photoluminescent layer. This design of the reflective structure will result in the light emitted from the four edge surfaces of the light-emitting semiconductor die to be reflected by the reflective structure back into the light-emitting semiconductor die. After multiple reflections inside the semiconductor die, the light can be guided toward and can escape from the top surface of the photoluminescent layer out of the CSP LED, therefore resulting in more light energy loss in the CSP LED and reducing the overall luminous efficacy.
In view of the above, there is a need to provide a solution suitable for a batch mass-production process to further improve the luminous efficacy of a CSP LED.